Combined mass spectrometer and ionization manometer

ABSTRACT

A mass spectrometer of the sector type which can be changed to an ionization manometer in which the ion collector current is a measure of the overall pressure of the gas to be analyzed utilizes a supply circuit for the system of accelerating electrodes in the ion source. The supply circuit provides the system of accelerating electrodes with a constant voltage or a pulsatory voltage in accordance with use as a mass spectrometer or an ionization manometer respectively.

United States Patent Inventor App]. No. Filed Patented Assignee Priority COMBINED MASS SPECTROME'IER AND IONIZATION MANOMETER 2 Claims, 3 Drawing Figs.

U.S. Cl 250/413 G, 250/419 SB, 250/419 ME, 324/33 Int. Cl H01j 39/34 I-Ielmut Wilhelm Werner Werner Emmasingel, Eindhoven, Netherlands Oct. 16, 1969 Oct. 5, 1

U.S. Philips Corporation New York, N.Y. Oct. 26, 1968 Netherlands 68 l 5 348 [50] Field of Search 250/41.9 SB, 41.9 G, 41.9 MB; 324/33 [56] References Cited UNITED STATES PATENTS 3,318,149 5/1967 Varadi 250/419 X 3,435,334 3/1969 Helmer..... 324/33 Primary Examiner-William F. Lindquist Attorney-Frank R. Trifari ABSTRACT: A mass spectrometer of the sector type which can be changed to an ionization manometer in which the ion collector current is a measure of the overall pressure of the gas to be analyzed utilizes a supply circuit for the system of accelerating electrodes in the ion source. The supply circuit provides the system of accelerating electrodes with a constant voltage or a pulsatory voltage in accordance with use as a mass spectrometer or an ionization manometer respectively.

EASURING M 24 DEVICE PATENTEDUCI 5l97l 3,610,922

I MEASURING 24 DEVICE MEASURlNG 24 DEVICE 25 SUPPLY CIRCUIT fig.3

CONSTANT VOLTAGE PULSATORY VOLTAGE SUPPLY DEVICE SUPPLY DEVICE INVENTOR.

HELMUT W. W. WERNER zdwzy w:

AGENT COMBINED MASS SPECTROMETER AND IONIZATION MANOMETER The invention relates to a mass spectrometer comprising an ion source which is provided with means to produce within the ion source ions of a gas to be analyzed and with a system of accelerating electrodes connected to a supply circuit to produce an electric field to extract the ions from the ion source through a narrow diaphragm aperture, which mass spectrometer comprises means to produce a sector field for the spatial separation of extracted ions of different types, and an ion collector to receive the extracted ions which describe a selected path in the sector field, said ion collector comprising means for measuring the ion collector current.

A type of mass spectrometers of the above mentioned kind is known in which the sector field for separating ions is a magnetic sector field. Another type is known in which the sector field for separating ions is an electrostatic sector field.

A mass spectrometer of the first-mentioned type, is described, for example by N. Warmoltz, D. Admiraal and E. Bouwmeester, in Elektronik 13, pp. 5-10 and 71.76, Jan. March, 1964. This mass spectrometer comprises an electromagnet for producing a magnetic sector field of 60. The supply circuit comprises a voltage source, by means of which a voltage which is substantially constant at least during a time corresponding to the transit time of the ions in the ion source is applied to the system of accelerating electrodes, so that in this mass spectrometer ions of substantially constant quotient of energy and charge are extracted from the ion source. In the magnetic sector field, said ions describe circular paths the radius of which is proportional to the square root from the quotient of the mass and the charge of the ions, so that substantially only ions with a given charge-to-mass ratio follow the selected path to the ion collector. The spectrum can be sensed by slow variation of the acceleration voltage or of the strength of the magnetic sector field. This mass spectrometer has a very stable and reliable operation and a good resolving power.

A mass spectrometer of the other mentioned type is described by J. Bracher in Zeitschrift fur angewandte Physik, Vol XIX Heft 4, 1965, pp. 347-348. This mass spectrometer comprises two coaxial cylindrical plates for producing an electrostatic sector field of 63.5". The supply circuit comprises a pulse generator by means of which a pulsatory voltage is applied to the system of accelerating electrodes, in which the duration of the voltage pulses is small with respect to the transit time of the ions in the ion source, so that in this mass spectrometer ions of a substantially constant quotient of momentum and charge are extracted from the ions source. In the electrostatic field said ions describe circular paths the radius of which is proportional to the quotient of the charge and the mass of the ions so that substantially only ions with a given charge-to-mass ratio follow the selected path to the ion collector. The spectrum can be sensed by slow variation of the pulse duration or of the pulse height or of the strength of the electrostatic sector field. The advantages of said spectrometer are the absence of a magnetic leakage field and the high'sensitivity. in addition, the low weight and the small dimensions make such a spectrometer particularly suitable for space research.

It is to be noted that hereinafter the brief expression constant voltage will be used. This expression will always have the meaning of the above expression a voltage which is substantially constant at least during a time corresponding to the transit time of the ions in the ion source. Furthermore the expression pulsatory voltage will be used. This expression will always have the meaning of the above expression pulsatory voltage in which the duration of the voltage pulses is small with respect to the transit time of the ions in the ion source".

It is desirable that during operation of the mass spectrometer as described above, the overall pressure in the ion source can be checked. ln the known above'mass spectrometer described by Warmoltz c.s. the ion source is provided for that purpose with a pipe branch which connects the ion source to a separate ionization manometer. The drawback of this is that the overall pressure is not determined exactly at the area of the ionization region. Furthermore there are the drawbacks which are inherent in the conventional ionization manometers, such as a disturbing effect as a result of X-rays.

It is the object of the invention to provide a mass spectrometer with which the said drawbacks are mitigated.

A mass. spectrometer of the kind stated in the first paragraph according to the invention is commutable into an ionization manometer, in. which the ion collector current is a measure of the overall pressure of the gas to be analyzed, by means of the said supply circuit, which for that purpose comprises means for supplying the system of accelerating electrodes with constant voltage or pulsatory voltage, as is desirable.

The mass spectrometer may comprise a magnet for producing a magnetic sector field. In the magnetic sector field the ions describe circular paths, the radius of which is proportional to the quotient of the momentum and the charge of the ions, which quotient is proportional to the square root from 4 the product of the quotient of the energy and the charge and the quotient of the mass and the charge. When constant voltage is applied to the system of accelerating electrodes, ions with constant quotient of energy and charge are extracted from the ion source and the device operates in known manner as a mass spectrometer. When in this mass spectrometer with a magnetic sector field pulsatory voltage is applied to the system of accelerating electrodes in the manner known for a mass spectrometer with an electrostatic sector field for the spatial separation of extracted ions, ions of constant quotient of momentum and charge are extracted from the ion source, so that all the ions in the magnetic sector field follow the selected path to the ion collector and the mass spectrometer operates as an overall pressure ionization manometer, in which the ion collector current is a measure of the overall pressure of the gas to be analyzed.

The mass spectrometer may also comprises a pair of two coaxial cylindrical plates for producing an electrostatic sector field. In the electrostatic sector field the ions describe circular paths the radius of which is proportional to the quotient of the energy and the charge of the ions, which quotient is proportional to the product of the square of the quotient of the momentum and the charge and the quotient of the charge and the mass. When pulsatory voltage is applied to the system of accelerating electrodes, ions with constant quotient of momentum and charge are extracted from the ion source and the device operates in known manner as a mass spectrometer. When in this mass spectrometer with an electrostatic sector field constant voltage is applied to the system of accelerating electrodes, in the manner which is known for a mass spectrometer with a magnetic sector field for the spatial separation of extracted ions, ions of substantially constant quotient of energy and charge are extracted from the ion source, so that all the ions in the electrostatic sector field follow the selected path to the ion collector and the mass spectrometer operates as an overall pressure ionization manometer, in which the ion collector current is a measure of the overall pressure of the gas to be analyzed.

In a device according to the invention it is avoided that upon measuring the overall pressure, A-rays from the part of the device where the ions are formed can reach the ion collector, so that particularly small gas pressures can be measured, while on the contrary in the conventional ionization manometers, the apparent ion collector current as a result of the secondary electrons liberated from the ion collector by X-rays differs from the true ion collector currents, and the contribution to the apparent ion-collector current as a result of said secondary current determinesa lower limit for the pressure to be measured.

In order that the invention may be readily carried into effect, it will now be described in greater detail, by way of example, with reference to the accompanying drawing, in which FIG. 1 is a cross-sectional view of an example of a mass spectrometer according to the invention.

FIG. 2 is a cross-sectional view of a second embodiment of a mass spectrometer according to the invention which comprises the same ion source as the spectrometer shown in FIG.

FIG. 3 is a cross-sectional view taken on the lines llIlII of the ion source shown in FIGS. 1 and 2 in which the supply circuit for the system of accelerating electrodes in the ion source is diagrammatically shown.

The mass spectrometer shown in FIG. 1 comprises an ion source which is denoted in its entirety by l, a separator section which is shown in its entirety by 2, and a detector device which is denoted in its entirety by 3. The evacuated ion source 1 comprises a wall 4 and a gas supply duct 5. Inside the ion source, ions are produced from the supplied gas by means of a beam 6 of electrons. The electrons are emitted by a cathode 7 and concentrated into a beam by means of a peak magnetic field produced by means of a magnet not shown. The beam 6 impinges on an electron collector 8 in front of which a diaphragm 9 is situated. Between the cathode 7 and the electron collector 8 a grid 10 for stabilization of the intensity of the electron beam is situated and a grid 11 by means of which the energy of the electrons can be varied. The electrodes 7, 8, 9, l and 11 are applied to supply voltages in normal manner not shown in the drawing. The ions produced by the electron beam 6 are extracted from the ion source through a narrow diaphragm slit 12 by means of an electric field applied by means of the electrodes l3, l4, l and 16. The supply circuit for the last-mentioned electrodes is not shown in FIG. 1. The ions extracted from the ion source enter the partly bent evacuated tube 17 which connects the ion source 11 to the evacuated part within the wall 18 of the detector device 3. In the tube 17 the ions enter a magnetic sector field which is produced by means of the magnet 19. The direction of the magnetic field is at right angles to the plane of the drawing. Within the wall 18, the diaphragms 20 and 21 and the ion collector 22 are situated. Only ions which substantially follow the selected path 23 reach the ion collector 22 which is connected to a measuring device 24, shown diagrammatically, for measuring the ion collector current. In FIG. 3, in which a crosssectional view of the ion source 1 is shown taken on the line lIlIIl of FIG. 1, the supply circuit 25 for supplying the electrodes ll, 12, 13 and 14 is diagrammatically shown. By means of the relays 26, 27, 28 and 29, the electrodes ll, l2, l3 and 14 are to be connected to the supply device 30 or the supply device 31. The supply device 30 supplies a constant voltage. The supply device 31 supplies a pulsatory voltage. When the electrodes 11, I2, 13 and 14, are connected to the supply device 30 for constant voltage, the extracted ions have substantially constant quotient of energy and charge and the ions in the magnetic sector field are separated according to quotient of momentum and charge, and therefore only ions with a given quotient of momentum and charge-which means with a given mass-to-charge-ratio, reach the collector 22 via the selected path 23. The device then operates as a mass spectrometer. When the electrodes 11, 12, 13, 14 are connected to the supply device 31 for pulsatory voltages, the extracted ions have a substantially constant quotient of momentum and charge and the ions in the magnetic sector field are not separated and therefore all the ions reach the collector 22 via the selected path 23. The device then operates as an overall pressure ionization manometer. In connection with the bent tube 17 and the diaphragms present, the ion collector is efiicaciously screened from X-rays from the ion source.

The mass spectrometer shown in FIG. 2 comprises the same ion source 1 as the mass spectrometer shown in FIG. 1 and also comprises the supply circuit shown in FIG. 3 and said mass spectrometer comprises the same detector device 3 as the mass spectrometer shown in FIG. 1 but has a different separator section 2. The separator section 2' comprises the tube 17' within which the ions enter an electrostatic sector field which is produced by the deflection plates 19'. Only the ions which follow substantially the selected path 23 reach the ion-collector 22 in the mass spectrometer. When in this mass spectrometer the electrodes 1 l, l2, l3 and I4 are connected to the supply device 31 for pulsatory voltage, the extracted ions have a substantially constant quotient of momentum and charge and the ions in the electrostatic sector field are separated according to quotient of energy and charge and therefore only ions having a given quotient of energy and charge-which means with a given mass-to-charge ratio reach the collector 22 via the selected path 23'. The device then operates as a mass spectrometer. When the electrodes ll, l2, l3 and 14 are connected to the supply device 30 for constant voltage, the extracted ions have substantially constant quotient of energy and charge and the ions in the electrostatic sector field are not separated and therefore all the ions reach the collector 22 via the selected path 23'. The device then operates as an overall pressure ionization manometer.

lclaim:

l. A mass spectrometer comprising an ion source which is provided with means to produce within the ion source ions of a gas to be analyzed and with a system of accelerating electrodes connected to a supply circuit to produce an electric field for extracting the ions from the ion source though a narrow diaphragm slit, said mass spectrometer further comprising means for producing an ion deflecting magnetic sector field for the spatial separation of extracted ions of different massto-charge ratios, and an ion collector for receiving the extracted ions which describe a selected path in said sector field, said ion collector further comprising means for measuring the ion collector current, the mass spectrometer being commutable, for operation as an ionization manometer in which the ion collector current is a measure of the overall pressure of the gas to be analyzed, by means of said supply circuit, said supply circuit supplying a constant voltage, at least during a time corresponding to the transit time of the ions in the ion source, for operation as a mass spectrometer, and a pulsatory voltage, in which the duration of the voltage pulses is small with respect to the transit time of the ions in the ion source, for operation as an ionization manometer.

2. A mass spectrometer comprising an ion source which is provided with means to produce within the ion source ions of a gas to be analyzed and with a system of accelerating electrodes connected to a supply circuit to produce an electric field for extracting the ions from the ion source through a narrow diaphragm slit, said mass spectrometer further comprising means for producing an ion deflecting electric sector field for the spatial separation of extracted ions of different mass-tocharge ratios, and an ion collector for receiving the extracted ions which describe a selected path in said sector field, said ion collector further comprising means for measuring the ion collector current, the mass spectrometer being commutable, for operation as an ionization manometer in which the ion collector current is a measure of the overall pressure of the gas to be analyzed, by means of said supply circuit, said supply circuit supplying a constant voltage, at least during a time corresponding to the transit time of the ions in the ion source, for operation as an ionization manometer, and a pulsatory voltage, in which the duration of the voltage pulses is small with respect to the transit time of the ions in the ion source, for operation as a mass spectrometer. 

2. A mass spectrometer comprising an ion source which is provided with means to produce within the ion source ions of a gas to be analyzed and with a system of accelerating electrodes connected to a supply circuit to produce an electric field for extracting the ions from the ion source through a narrow diaphragm slit, said mass spectrometer further comprising means for producing an ion deflecting electric sector field for the spatial separation of extracted ions of different mass-to-charge ratios, and an ion collector for receiving the extracted ions which describe a selected path in said sector field, said ion collector further comprising means for measuring the ion collector current, the mass spectrometer being commutable, for operation as an ionization manometer in which the ion collector current is a measure of the overall pressure of the gas to be analyzed, by means of said supply circuit, said supply circuit supplying a constant voltage, at least during a time corresponding to the transit time of the ions in the ion source, for operation as an ionization manometer, and a pulsatory voltage, in which the duration of the voltage pulses is small with respect to the transit time of the ions in the ion source, for operation as a mass spectrometer. 